API "POST" shows successful but won't reflect changes on database - php

Question

I have a basic web application that has been coded in php.
The app carries out CRUD operations by making use of an API made through PHP. When I try to use my update.php API endpoint, I get a successful response but no changes reflect in db.
Project Structure
Project_Structure
update.php in api/mailbox
<?php
// include database and object files
include_once '../config/database.php';
include_once '../objects/mailbox.php';
// get database connection
$database = new Database();
$db = $database->getConnection();
// prepare mailbox object
$mailbox = new Mailbox($db);
//For diagnostics
$data = json_decode(file_get_contents('php://input'), true);
print_r($data);
echo $data[""];
// set ID property of product to be edited
$mailbox_id->mailbox_id = $data->mailbox_id;
// set mailbox property values
$mailbox->username = $_POST['username'];
$mailbox->password = base64_encode($_POST['password']);
$mailbox->name = $_POST['name'];
$mailbox->quota = $_POST['quota'];
$mailbox->modified = date('Y-m-d H:i:s');
$mailbox->active = $_POST['active'];
$mailbox->mailbox_id = $_POST['mailbox_id'];
// create the mailbox
if($mailbox->update()){
$mailbox_arr=array(
"status" => true,
"message" => "Successfully Updated Mailbox"
);
}
else{
$mailbox_arr=array(
"status" => false,
"message" => "Mailbox already exists!"
);
}
print_r(json_encode($mailbox_arr));
?>
mailbox.php(in objects folder)
// update mailbox
function update(){
$query = "UPDATE
". $this->table_name ."
SET
username='".$this->username."', password='".$this->password."', name='".$this->name."', quota='".$this->quota."', modified='".$this->modified."', active='".$this->active."'
WHERE
mailbox_id= '".$this->mailbox_id."'";
// prepare query
$stmt = $this->conn->prepare($query);
// execute query
if($stmt->execute()){
return true;
}
return false;
}
update.php (The rendered page, on clicking update, the error is: **Mailbox already exists)**
<?php
$content = '<div class="container"
<div class="row">
<!-- left column -->
<div class="col-md-12">
<!-- general form elements -->
<div class="box box-primary">
<div class="box-header with-border">
<h3 class="box-title">Update Mailbox</h3>
</div>
<!-- /.box-header -->
<!-- form start -->
<form role="form">
<div class="box-body">
<div class="form-group">
<div class="form-group">
<label for="exampleMBID1">Mailbox ID</label>
<input type="text" class="form-control" id="mailbox_id" placeholder="Mailbox ID" disabled>
</div>
<label for="exampleInputUserName1">User Name</label>
<input type="text" class="form-control" id="username" placeholder="Enter Username e.g jsmith">
</div>
<div class="form-group">
<label for="exampleInputPassword1">Password</label>
<input type="password" class="form-control" id="password" placeholder="Enter Password">
</div>
<div class="form-group">
<label for="exampleInputName1">Name</label>
<input type="text" class="form-control" id="name" placeholder="Name of User">
</div>
<div class="form-group">
<label for="exampleInputMaildir1">Maildir</label>
<input type="text" class="form-control" id="maildir" placeholder="Enter Maildir" disabled>
</div>
<div class="form-group">
<label for="exampleInputQuota1">Quota (0=Unlimited)</label>
<input type="text" class="form-control" id="quota" placeholder="Enter Quota">
</div>
<div class="form-group">
<label for="examplelocalpart1">Local Part</label>
<input type="text" class="form-control" id="local_part" placeholder="localpart" disabled>
</div>
<div class="form-group">
<label for="exampledomain1">Domain</label>
<input type="text" class="form-control" id="domain" placeholder="domain" disabled>
</div>
<div class="form-group">
<label for="examplecreated1">Created</label>
<input type="text" class="form-control" id="created" placeholder="Created" disabled>
</div>
<div class="form-group">
<label for="examplemodified1">Modified</label>
<input type="text" class="form-control" id="modified" placeholder="Modified">
</div>
<div class="form-group">
<label for="exampleactive1">Active (0=Not Active, 1=Active)</label>
<input type="text" class="form-control" id="active" placeholder="Enter 0 or 1">
</div>
</div>
<!-- /.box-body -->
<div class="box-footer">
<input type="button" class="btn btn-primary" onClick="UpdateMailbox()" value="Update"></input>
</div>
</form>
</div>
<!-- /.box -->
</div>
</div>
</div>';
include('../master.php');
?>
<script>
$(document).ready(function(){
$.ajax({
type: "GET",
url: "../api/mailbox/read_single.php?mailbox_id=<?php echo $_GET['mailbox_id']; ?>",
dataType: 'json',
success: function(data) {
$('#username').val(data['username']);
$('#password').val(data['password']);
$('#name').val(data['name']);
$('#maildir').val(data['maildir']);
$('#quota').val(data['quota']);
$('#local_part').val(data['local_part']);
$('#domain').val(data['domain']);
$('#created').val(data['created']);
$('#modified').val(data['modified']);
$('#active').val(data['active']);
$('#mailbox_id').val(data['mailbox_id']);
},
error: function (result) {
console.log(result);
},
});
});
function UpdateMailbox(){
$.ajax(
{
type: "POST",
url: '../api/mailbox/update.php',
dataType: 'json',
data: {
mailbox_id: <?php echo $_GET['mailbox_id']; ?>,
username: $("#username").val(),
password: $("#password").val(),
name: $("#name").val(),
maildir: $("#maildir").val(),
quota: $("#quota").val(),
domain: $("#domain").val(),
modified: $("#modified").val(),
active: $("#active").val()
},
error: function (result) {
alert(result.responseText);
},
success: function (result) {
if (result['status'] == true) {
alert("Successfully Updated Mailbox!");
window.location.href = '/MailEasy/mailbox/listAll.php';
}
else {
alert(result['message']);
}
}
});
}
</script>
1) Why is not updating when using web UI?
2) When using postman, it shows successful, why are requests not reaching the database?
Postman --> Successful response but no changes in db.
Php webpage --> Mailbox already exists.
Thank you